To accurately reproduce a desired target color using a printing system, an operator must perform repeated color adjustments by trial and error. In particular, the operator might adjust the color of an image on a video display in an attempt to obtain the desired target color on a color printer. After printing that first image using the color printer, the operator must perform a second color adjustment on the video display, wherein the adjustments are based on observations of the first printed image. This process would be repeated until the desired color print is output.
Such trial and error generally involves the process of color separation. In the past, color separation has traditionally been a matter of deciding what quantities of each of several inks (or other colorants) to use to achieve a given color. While this functionality was originally a photochemical process involving colored filters, it has evolved to its current state, which utilizes look-up tables comprising colorimetric input values or input values in a device color space. The output values for the tables may be n-dimensional ink vectors, where n is the number of inks used by the printer and the vector components represent quantities of each ink available on the color printer. In practice, the current approach utilizes these tables to transform ink amounts for each color plane, thereby reproducing the desired target color.
However, controlling print color by variation of ink amounts is a highly non-linear process, deriving from a complex relationship between changes in the quantity of each ink color used and the color of the resulting printed ink combination. As a result of this non-linearity, the gamut (the set of all printable colors) of a printing device may also include concavities when plotted in a three dimensional color space. These concavities in some cases result in only relatively dull dark colors being printable. In addition, small changes in a system comprising non-linear relationships may also result in unacceptably large changes in output color. Therefore, non-linear relationships in a printing system may make it very challenging to obtain printing properties such as smooth transitions between colors, cost per copy, color constancy, and grain.
Therefore, there is a need for improving color printing in a printing system. Further, there is a need for color reproduction accuracy, minimized ink usage, improved spectral printing, and highly dynamic printing ranges.